This application claims priority to an application entitled xe2x80x9cIntermodulation Control Device and Method in Mobile Communication Systemxe2x80x9d filed in the Korean Industrial Property Office on Dec. 29, 1999 and assigned Serial No. 99-64546, the contents of which are hereby incorporated by reference.
1. Field of the Invention
The present invention relates generally to an IMD (Intermodulation) control device and method in a mobile communication system, and in particular, to an IMD control device and method using a switch.
2. Description of the Related Art
Single tone desensitization and intermodulation spurious response attenuation are significant factors in designing a mobile station in the RF (Radio Frequency) field. In many cases, these two factors cause current consumption in designing a receiver and increase the cost of terminal parts. Therefore, research has been made on methods of increasing the performance of a mobile station with low current consumption, to satisfy minimum performance standards related to these factors.
Regarding the intermodulation spurious response attenuation that falls into the field related to the present invention, its minimum performance standards (e.g., IS-98A Receiver Performance Intermodulation Spurious Response Attenuation Test shown in Table 1) are specified in three items in the table. The three items differ in frequency band. For example, only one item applies to the PCS (Personal Communication Services) frequency band and the three items apply to the CDMA (Code Division Multiple Access) frequency band, 900 MHz due to the dual mode of CDMA and AMPS (Advanced Mobile Phone System). For PCS, a circuit used for single tone desensitization also satisfies the intermodulation item. However, two of the three items must be additionally controlled for CDMA. The second item of xe2x88x9232 dBm can be satisfied by controlling current flowing through an IF (Intermediate Frequency) amplifier, whereas it is impossible to satisfy the third item of xe2x88x9221 dBM through current control alone. To satisfy the third item, it is necessary to eliminate a high level harmonic component by reducing the power level of a received signal (a dual-tone signal in the test), thus reducing the influence of the harmonic component.
FIGS. 1, 2, and 3 are block diagrams of conventional IMD control devices to eliminate a high level harmonic component. The conventional IMD control device shown in FIG. 1 has a diode 124 connected between a duplexer 104 and an LNA (Low Noise Amplifier) 106 above a ground terminal to reduce the power level of an input signal. Another conventional IMD control device shown in FIG. 2 has a diode 126 connected between a SAW (Surface Acoustic Wave Filter) 108 and a mixer 116 above the ground terminal to reduce the power level of an input signal. A third conventional IMD control device shown in FIG. 3 has a switch 128 connected to the LNA 106 in parallel to reduce the power level of an input signal. The three conventional IMD control devices aim at minimization of harmonic influence caused by intermodulation between the LNA 106 and the IF amplifier 118 by reducing the power levels of input signals.
The above conventional IMD control devices perform IMD control only at an RF end, that is, at an LNA. The IMD control of the LNA causes great current consumption (e.g., 10 mA) at an IF amplifier and makes it impossible to optimize the performance of a mobile station.
It is, therefore, an object of the present invention to provide an IMD control device and method in a mobile communication system to overcome the problems of conventional control devices.
It is another object of the present invention to provide a device and method for reducing current consumption during an IMD control operation in order to minimize the influence of IMD in a mobile station.
It is a further object of the present invention to provide an IMD control device and method for optimizing the performance of a mobile station.
To achieve the above and other objects, in an IMD control device for a mobile communication system, an LNA performs low noise amplification on an input RF signal, a first switch is connected to the LNA in parallel, for switching according to a first control signal received for IMD control, a frequency converter down-converts the output of the LNA to an IF signal, an IF amplifier amplifies the IF signal, a second switch is connected in parallel to the IF amplifier, for switching according to a second IMD control signal received for IMD control, and a controller generates the IMD control signals at voltage levels determined according to an RSSI and an energy to noise ratio.